Physiology MCQ Answer 94
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The Poiseuille-Hagen formula is the mathematical expression of the relation between the flow in a long narrow tube, the viscosity of the fluid & the radius of the tube.
F = (PA – PB) x p x 1 x r4
8 h L
Where:
F = flow;
PA – PB = pressure difference between the 2 ends of the tube;
h = viscosity;
r = radius of tube;
L = length of tube;
Since flow is equal to pressure difference divided by resistance,
R = 8hL
pr4
ie. flow varies directly & resistance inversely with radius to power of 4.
\ blood flow is affected markedly by small changes in calibre of vessels.
If, for example, there is:
19% increase in radius of blood vessel Þ
flow thru a vessel is doubled;
when radius is doubled, resistance is reduced to
6% of its previous value.
This is why organ blood flow is so effectively regulated by small changes in calibre of arterioles.
Category: Physiology MCQs
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